Axial flow positive displacement gas generator with combustion extending into an expansion section

ABSTRACT

An axial flow positive displacement engine has an inlet axially spaced apart and upstream from an outlet. Inner and outer bodies have offset inner and outer axes extend from the inlet to the outlet through first, second, and third sections of a core assembly in serial downstream flow relationship. At least one of the bodies is rotatable about its axis. The inner and outer bodies have intermeshed inner and outer helical blades wound about the inner and outer axes respectively. The inner and outer helical blades extend radially outwardly and inwardly respectively and have first, second, and third twist slopes in the first, second, and third sections respectively. The first twist slopes are less than the second twist slopes and the third twist slopes are less than the second twist slopes. A combustion section extends axially downstream from the second section through at least a portion of the third section.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates generally to turbomachinery and gasgenerators and, more particularly, to axial flow positive displacementgas generators.

Gas generators are used in gas turbine engines such as in core enginesfor turbofan and other gas turbine engines having in downstream flowrelationship a compressor section, a combustion section, and a turbinesection. The function of the gas generator is to provide high energyfluid, which can in turn be harnessed to provide power for a variety ofapplications. Axial flow gas generators are particularly useful in manyturbomachinery applications. Turbomachinery based gas generators areutilized in a wide range of applications owing in a great deal to acombination of desirable attributes such as high specific energy exhauststream (energy per unit mass), high mass flow rate for a given frontalarea, continuous, near steady fluid flow, reasonable thermal efficiencyover a wide range of operating conditions. It is a goal of the gasturbine manufacturers to have light weight and highly efficient gasgenerators. It is another goal to have as few parts as possible in thegas generator to reduce the costs of manufacturing, installing,refurbishing, overhauling, and replacing the gas generator. Therefore,it is desirable to have a gas generator that improves all of thesecharacteristics of gas generators.

BRIEF DESCRIPTION OF THE INVENTION

An axial flow positive displacement engine, such as a positivedisplacement axial flow gas generator, includes an inlet axially spacedapart and upstream from an outlet. Inner and outer bodies having offsetinner and outer axes respectively extend from the inlet to the outlet.Either or both bodies may be rotatable. In one embodiment of thegenerator, the inner body is rotatable about the inner axis within theouter body. The outer body may be rotatably fixed or rotatable about theouter axis. The inner and outer bodies have intermeshed inner and outerhelical blades wound about inner and outer axes respectively. The innerand outer helical blades extend radially outwardly and inwardlyrespectively.

The helical blades have first, second, and third twist slopes in thefirst, second, and third sections, respectively. A twist slope isdefined as the amount of rotation of a cross-section of the helicalelement per unit distance along an axis. The first twist slopes are lessthan the second twist slopes and the third twist slopes are less thanthe second twist slopes. A combustion section extends axially downstreamfrom the end of the first section through the second section into atleast a portion of the third section. Constant volume combustion occursin the second section.

The helical blades in the first section have sufficient number of turnsto trap charges of air in the first section during the generator'soperation. In one embodiment of the gas generator, the number of turnsis enough to mechanically trap the charges of air. In another embodimentof the gas generator, the number of turns is enough to dynamically trapthe charges of air.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view illustration of an exemplary aircraftgas turbine engine with a positive displacement axial flow gasgenerator.

FIG. 2 is a diagrammatic cross-sectional view illustration of thepositive displacement gas generator with a combustion section extendingthrough a portion of an expansion section of the gas generatorillustrated in FIG. 1.

FIG. 3 is a diagrammatic partially cut away perspective viewillustration of helical portions of inner and outer bodies of the gasgenerator illustrated in FIG. 2.

FIG. 4 is a diagrammatic cross-sectional view illustration of gearingbetween inner and outer bodies of the gas generator illustrated in FIG.3.

FIG. 5 is a diagrammatic cut away perspective view illustration of thehelical portions of inner and outer bodies of the gas generatorillustrated in FIG. 3.

FIG. 6 is a diagrammatic cross-sectional view illustration of the innerand outer bodies taken through 6-6 in FIG. 4.

FIGS. 7-10 are diagrammatic cross-sectional view illustrations of analternate inner and outer body configuration at different inner bodyrelative angular positions.

FIG. 11 is a diagrammatic view illustration of a T S temperature-entropydiagram illustrating a cycle of the gas generator illustrated in FIG. 2.

DETAILED DESCRIPTION OF THE INVENTION

Illustrated in FIG. 1 is an exemplary embodiment of an axial flowpositive displacement engine 8 illustrated herein as a gas generator idin a gas turbine engine 100 application in which the gas generator 10 isused to power a turbine that produces work to drive a fan 108 in a fansection of the engine 100. The gas generator 10 may be used to directlydrive power consuming devices such as marine propulsion drives andelectrical power generators or aircraft nozzles or fans. The exemplaryembodiment of the gas turbine engine 100 illustrated in FIG. 1 is anaircraft gas turbine engine having a core engine 118 including the gasgenerator 10 downstream of the fan section 112. Combustion gases aredischarged from the gas generator 10 into a low pressure turbine (LPT)120 having a row of low pressure turbine rotor blades 122. The lowpressure turbine rotor blades 122 are drivingly attached to a row ofcircumferentially spaced apart fan rotor blades 130 of the fan 108 inthe fan section 112 by a low pressure shaft 132 to form a low pressurespool 134 circumscribing an engine centerline 136. The gas generator 10may be used in other applications including but not limited to groundbased industrial and marine gas turbine engines.

Referring to FIGS. 2-5, the gas generator 10 includes a core assembly 15including inner and outer bodies 12, 14 extending from an inlet 20 to anoutlet 22. The inner body 12 is disposed within a cavity 19 of the outerbody 14. The inner and outer bodies 12, 14 have inner and outer axes 16,18 respectively. The core assembly 15 has first, second, and thirdsections 24, 26, 28 in serial downstream flow relationship. A combustionsection 40 extends axially downstream from the end of the first section24 through the second section 26 into at least a portion of the thirdsection 28. Illustrated herein is the combustion section 40 extendingaxially downstream from the end of the first section 24 through aportion of the third section 28 indicated by an expansion-combustionportion 42. The core assembly 15 has continuous flow through the inlet20 and the outlet 22.

Individual charges of air 50 are captured in and by the first section24. Compression of the charges 50 occurs as the charges 50 pass from thefirst section 24 to the second section 26. Thus, an entire charge 50undergoes compression while it is in both the first and second sections24 and 26, respectively. Combustion begins in the second section 26after the entire charge 50 has passed out of the first section 24 intothe second section 26 and the combustion in the second section 26 isconstant volume combustion. Combustion continues into and at leastpartially through the third section 28 which is an expansion sectionand, thus, extracts energy from the combusted and combusting charges ofair 50 to power the first and second sections 24, 26, respectively.Combustion may continue through the entire third section 28. Expansionof the charges 50 occurs as the charges 50 pass from the second section26 to the third section 28. Thus, the entire charge 50 undergoesexpansion while it is in both the second and third sections 26 and 28.

A Murrow cycle with combustion occurring between the second and thirdsections 26, 28 provides isenthalpic expansion yielding better gasgenerator efficiency as compared to a gas generator which has combustiononly in the second section 26. The Murrow cycle engine has greaterthermal efficiency than a Brayton cycle engine and a greater net workcapability than a Brayton cycle engine. Either or both bodies may berotatable and, if both bodies are rotatable, they rotate in the samecircumferential direction clockwise or counterclockwise at differentrotational speeds determined by a fixed relationship. In one embodimentof the generator, the inner body 12 is rotatable about the inner axis 16within the outer body 14 and the outer body 14 may be rotatably fixed orrotatable about the outer axis 18.

The inner and outer bodies 12, 14 have intermeshed inner and outerhelical elements wound about the inner and outer axes 16, 18,respectively. The elements are inner and outer helical blades 17 and 27having inner and outer helical surfaces 21 and 23, respectively. Theinner helical blades 17 extend radially outwardly from a hollow innerhub 51 of the inner body 12 and the outer helical blades 27 extendradially inwardly from an outer shell 53 of the outer body 14. An innerhelical edge 47 along the inner helical blade 17 sealingly engages theouter helical surface 23 of the outer helical blade 27 as they rotaterelative to each other. An outer helical edge 48 along the outer helicalblade 27 sealingly engages the inner helical surface 21 of the innerhelical blade 17 as they rotate relative to each other.

Illustrated in FIG. 4 is a longitudinal cross-section taken through theinner and outer bodies 12, 14. The inner and outer bodies 12, 14 areillustrated in axial cross-section in FIG. 6. The inner body 12 isillustrated herein as having two inner body lobes 60 which correspond totwo inner helical blades 17 and which results in a football or pointedoval-shaped inner body cross-section 69. The outer body 14 has threeouter body lobes 64 which corresponds to three outer helical blades 27(illustrated in FIGS. 3 and 4). Note that 3 sealing points 62 betweenthe inner and outer bodies 12 and 14 are illustrated in FIG. 6 but thatthere is continuous sealing between the inner and outer helical blades17 and 27 along the length of the inner and outer bodies 12, 14.

An alternative configuration of the inner and outer bodies 12, 14 isillustrated in cross-section in FIGS. 7-10. The inner body 12 isillustrated therein as having three inner body lobes 60 which correspondto three inner helical blades 17 which results in a triangularly-shapedinner body cross-section 68 as illustrated in FIG. 7. The outer body 14has two outer body lobes 64 which corresponds to two outer helicalblades 27. In general, if the inner body 12 has N number of lobes theouter body 14 will have N+1 or N−1 lobes. Note that 5 sealing points 62between the inner and outer bodies 12 and 14 are illustrated in FIG. 7but that there is continuous sealing between the inner and outer helicalblades 17 and 27 along the length of the inner and outer bodies 12, 14.

Referring to FIG. 5, the helical elements have constant first, second,and third twist slopes 34, 36, 38 in the first, second, and thirdsections 24, 26, 28, respectively. A twist slope A is defined as theamount of rotation of a cross-section 41 of the helical element (such asthe oval-shaped or triangularly-shaped inner body cross-sections 69 and68 illustrated in FIGS. 6 and 7, respectively) per distance along anaxis such as the inner axis 16 as illustrated in FIG. 5. Illustrated inFIG. 5 is 360 degrees of rotation of the inner body cross-section 41.The twist slope A is also 360 degrees or 2 Pi radians divided by anaxial distance CD between two adjacent crests 44 along the same inner orouter helical edges 47 and 48 of the helical element such as the inneror outer helical blades 17 or 27 as illustrated in FIG. 5. The axialdistance CD is the distance of one full turn 43 of the helix.

The twist slope A of the inner element in each of the sections isdifferent from the twist slope A of the outer element. The ratio of thetwist slope A of the outer body 14 to the twist slope A of the innerbody 12 is equal to the ratio of the number of inner helical blades 17blades on the inner body 12 to the number of outer helical blades 27blades on the outer body 14. The first twist slopes 34 are less than thesecond twist slopes 36 and the third twist slopes 38 are less than thesecond twist slopes 36. One might also describe the helical elements interms of helical angle. The helical elements have constant first,second, and third helical angles corresponding to the constant first,second, and third twist slopes 34, 36, 38 in the first, second, andthird sections 24, 26, 28, respectively, in much the same way one woulddescribe a screw in terms of pitch and pitch angle.

Referring again to FIGS. 3-5, the inner helical blade 17 in the firstsection 24 has a sufficient number of turns 43 to trap the charges ofair 50 in the first section 24 during the generator's operation. Thetrapped charges of air 50 allow positive displacement compression sothat higher pressures developed downstream cannot force air or thecharges back out the inlet 20. In one embodiment of the gas generator,the number of turns 43 in the first section 24 is enough to mechanicallytrap the charges of air 50. In another embodiment of the gas generator10, the number of turns 43 in the first section 24 is enough todynamically trap the charges of air 50. Mechanically trapped means thatthe charge 50 is trapped by being closed off from the inlet 20 at anupstream end 52 of the charge 50 before it passes into the secondsection 26 at a downstream end 54 of the charge 50. Dynamically trappedmeans that though the downstream end 54 of the trapped charge may havepassed into the second section 26, the upstream end 52 of the charge hasnot yet completely closed. However, at its downstream end 54 by the timea pressure wave from the second section travels to the inlet 20,relative rotation between the bodies will have closed off the trappedcharge of air 50 at its upstream end 52.

For the fixed outer body 14 embodiment, the inner body 12 is crankedrelative to the outer axis 18 so that as it rotates about the inner axis16, the inner axis 16 orbits about the outer axis 18 as illustrated inFIGS. 7-10. The inner body 12 is illustrated as having been rotatedabout the inner axis 16 from its position in FIG. 7 to its position inFIG. 8 and the inner axis 16 is illustrated as having orbited about theouter axis 18 about 90 degrees. The inner and outer bodies 12, 14 aregeared together so that they always rotate relative to each other at afixed ratio as illustrated by gearing in gearbox 82 in FIGS. 1 and 4.

If the outer body 14 in FIG. 7 was not fixed, then it would rotate aboutthe outer axis 18 at 1.5 times the rotational speed that the inner body12 rotates about the inner axis 16. The inner body 12 rotates about theinner axis 16 with an inner body rotational speed 74 equal to itsorbital speed 76 divided by the number of inner body lobes. The numberof inner lobes are equal the number of blades. If the inner body 12rotates in the same direction as its orbital direction a 2 lobed outerbody configuration is used. If the inner body 12 rotates in an oppositeorbital direction a 4 lobed outer body configuration is used.

The twist slopes of the outer body 14 are equal to the twist slopes ofthe inner body 12 times the number of inner body lobes N divided by thenumber of outer body lobes M. For the configuration illustrated in FIGS.7-10 having three inner lobes or inner helical blades 17 and two outerlobes or outer helical blades 27, it takes 900 degrees of rotation ofthe outer body 14 and 600 degrees of rotation of the inner body 12 tomechanically capture one of the charges of air 50. The inner body twistslope is substantially increased going from the first section 24 to thesecond section 26. This axial location is designated the compressionplane as indicated in FIG. 2. Combustion begins in the second section 26when an upstream end of the charge of air 50 crosses the compressionplane. Each of the charges is combusted individually and, because thetwist slopes in the inner and outer bodies remain constant through thesecond section 26, there is constant volume combustion in the secondsection 26.

Referring to FIGS. 2-4, following the constant volume combustion in thesecond section 26, the charge or working fluid undergoes an isenthalpicexpansion-combustion process between the second and third sections 26and 28. Work is extracted at the same rate as heat is added wherecombustion takes place in the expansion-combustion portion 42 which mayinclude the entirety of the third section 28. After the leading edge ofthe high temperature and high pressure charge crosses the expansionplane, the volume of the charge of air 50 begins to expand and growaxially. This expansion extracts energy from the fluid, providing thework necessary to drive the first section 24 and the second section 26and sustain the gas generating process. Following expansion, the fluidis discharged across the rear plane into a downstream plenum atsubstantially elevated temperature and pressure relative to its initialstate. In addition to isenthalpic expansion between the second and thirdsections 26 and 28, a remaining work requirement is met through a nearlyisentropic expansion between the second and third sections. FIG. 10illustrates a temperature-entropy diagram (T-S diagram) of a Murrowcycle versus a Brayton cycle. The Murrow cycle is a thermodynamic cycleof the axial flow positive displacement engine 8 with isenthalpicexpansion process and nearly isentropic expansion between the second andthird sections 26 and 28.

The Murrow cycle inputs work into the compression stage of the cycle,denoted as Wcmp, for compression. The Murrow cycle inputs work, denotedas Wcmb, into the constant volume combustion stage of the cycle andinputs heat, denoted as Qcmb1, for initial combustion. The Murrow cycleinputs heat, denoted as Qcmb2, and extracts work isenthalpically,denoted as Wh, during the first portion of the expansion stage of thecycle. The Murrow cycle extracts work adiabatically, denoted as Wa,during the remaining portion of the expansion stage of the cycle intothe third section 28 of the engine 8. In the exemplary embodiment of theMurrow cycle engine illustrated herein, first and second sections 24, 26functions as a compressor of the engine 8. In the exemplary embodimentof the Murrow cycle engine illustrated herein, the second and thirdsections 26, 28 function as a turbine of the engine 8 and input workinto both the first and second sections 24, 26.

The Murrow cycle allows for a reasonable amount of isenthalpicexpansion-combustion to occur while preserving the thermal boundaryconditions of a downstream component, such as a low pressure turbine orexhaust nozzle as illustrated in FIG. 1. The net work gain realizedthrough the isenthalpic expansion process and the additional heat inputduring the isenthalpic expansion leads to thermal efficiencyimprovements over a steady flow positive displacement engine withoutisenthalpic expansion as disclosed in U.S. patent application Ser. No.(ATTORNEY DOCKET NUMBER 177664). Net work of the Murrow cycle engine asillustrated in FIG. 11 is Wm and the net work of the Brayton cycle isWb. The net work of the Murrow and Brayton cycles are referenced toinlet pressure of the engine 8 indicated by a constant pressure line inFIG. 11. The Murrow cycle may also include combustion through theentirety of the expansion or third section 28.

This new thermodynamic cycle for a positive displacement engine or gasgenerator with isenthalpic expansion offers substantial performancebenefits over the steady flow positive displacement engine or gasgenerator without isenthalpic expansion in terms of both net work andthermal efficiency. Isenthalpic expansion offers the potential to bringexhaust gas temperatures up to Brayton levels while retaining asignificantly elevated exhaust gas pressure. The engine and cycle withisenthalpic expansion is conceptually implemented by extending thecombustion process through at least a portion of the third section 28.The ability to increase net work over that of the Brayton cycle willallow the same power requirement to be met with a smaller engine or gasgenerator, making the combination particularly attractive for weight andsize sensitive applications.

While there have been described herein what are considered to bepreferred and exemplary embodiments of the present invention, othermodifications of the invention shall be apparent to those skilled in theart from the teachings herein and, it is therefore, desired to besecured in the appended claims all such modifications as fall within thetrue spirit and scope of the invention. Accordingly, what is desired tobe secured by Letters Patent of the United States is the invention asdefined and differentiated in the following claims.

1. An axial flow positive displacement engine comprising: an inletaxially spaced apart and upstream from an outlet, a core assemblyincluding an inner body disposed within an outer body and the inner andouter bodies extending from the inlet to the outlet, the inner and outerbodies having offset inner and outer axes respectively, at least one ofthe inner and outer bodies being rotatable about a corresponding one ofthe inner and outer axes, the inner and outer bodies having intermeshedinner and outer helical blades wound about the inner and outer axesrespectively, the inner and outer helical blades extending radiallyoutwardly and inwardly respectively, the core assembly having first,second, and third sections in serial downstream flow relationshipextending between the inlet and the outlet, the inner and outer helicalblades having first, second, and third twist slopes in the first,second, and third sections respectively, the first twist slopes beingless than the second twist slopes and the third twist slopes being lessthan the second twist slopes, and a combustion section extending axiallydownstream from the second section through at least a portion of thethird section.
 2. An engine as claimed in claim 1 further comprising theinner helical blade in the first section having a sufficient number ofturns to trap charges of air in the first section during the generator'soperation.
 3. An engine as claimed in claim 2 further comprising thenumber of turns being enough to mechanically trap the charges of air. 4.An engine as claimed in claim 2 further comprising the number of turnsbeing enough to dynamically trap the charges of air.
 5. An engine asclaimed in claim 1 further comprising the outer body being rotatableabout the outer axis and the inner body and being rotatable about theinner axis.
 6. An engine as claimed in claim 5 further comprising theinner and outer bodies being geared together in a fixed gear ratio. 7.An engine as claimed in claim 6 further comprising the inner helicalblade in the first section having a sufficient number of turns to trapcharges of air in the first section during the generator's operation. 8.An engine as claimed in claim 7 further comprising the number of turnsbeing enough to mechanically trap the charges of air.
 9. An engine asclaimed in claim 7 further comprising the number of turns being enoughto dynamically trap the charges of air.
 10. An engine as claimed inclaim 1 further comprising the outer body being rotatably fixed aboutthe outer axis and the inner body being orbital about the outer axis.11. An engine as claimed in claim 10 further comprising the innerhelical blade in the first section having a sufficient number of turnsto trap charges of air in the first section during the generator'soperation.
 12. An engine as claimed in claim 11 further comprising thenumber of turns being enough to mechanically trap the charges of air.13. An engine as claimed in claim 12 further comprising the number ofturns being enough to dynamically trap the charges of air.
 14. A gasturbine engine comprising: a gas generator connected in work producingrelationship to a power consuming device, the gas generator including aninlet axially spaced apart and upstream from an outlet, a core assemblyincluding an inner body disposed within an outer body and the inner andouter bodies extending from the inlet to the outlet, the inner and outerbodies having offset inner and outer axes respectively, at least one ofthe inner and outer bodies being rotatable about a corresponding one ofthe inner and outer axes, the inner and outer bodies having intermeshedinner and outer helical blades wound about the inner and outer axesrespectively, the inner and outer helical blades extending radiallyoutwardly and inwardly respectively, the core assembly having first,second, and third sections in serial downstream flow relationshipextending between the inlet and the outlet, the inner and outer helicalblades having first, second, and third twist slopes in the first,second, and third sections respectively, the first twist slopes beingless than the second twist slopes and the third twist slopes being lessthan the second twist slopes, and a combustion section extending axiallydownstream from the second section through at least a portion of thethird section.
 15. An engine as claimed in claim 14 further comprisingthe inner helical blade in the first section having a sufficient numberof turns to trap charges of air in the first section during thegenerator's operation.
 16. An engine as claimed in claim 15 furthercomprising the number of turns being enough to mechanically trap thecharges of air.
 17. An engine as claimed in claim 15 further comprisingthe number of turns being enough to dynamically trap the charges of air.18. An engine as claimed in claim 14 further comprising the outer bodybeing rotatable about the outer axis and the inner body and beingrotatable about the inner axis.
 19. An engine as claimed in claim 18further comprising the inner and outer bodies being geared together in afixed gear ratio.
 20. An engine as claimed in claim 19 furthercomprising the inner helical blade in the first section having asufficient number of turns to trap charges of air in the first sectionduring the generator's operation.
 21. An engine as claimed in claim 20further comprising the number of turns being enough to mechanically trapthe charges of air.
 22. An engine as claimed in claim 20 furthercomprising the number of turns being enough to dynamically trap thecharges of air.
 23. An engine as claimed in claim 14 further comprisingthe outer body being rotatably fixed about the outer axis and the innerbody being orbital about the outer axis.
 24. An engine as claimed inclaim 23 further comprising the inner helical blade in the first sectionhaving a sufficient number of turns to trap charges of air in the firstsection during the generator's operation.
 25. An engine as claimed inclaim 24 further comprising the number of turns being enough tomechanically trap the charges of air.
 26. An engine as claimed in claim25 further comprising the number of turns being enough to dynamicallytrap the charges of air.
 27. An aircraft gas turbine engine comprising:a fan section and a core engine including a gas generator downstream ofthe fan section, a low pressure turbine having at least one row of lowpressure turbine rotor blades downstream of the gas generator, the lowpressure turbine drivingly attached to at least one row ofcircumferentially spaced apart fan rotor blades in the fan section by alow pressure shaft, the gas generator including an inlet axially spacedapart and upstream from an outlet, a core assembly including an innerbody disposed within an outer body and the inner and outer bodiesextending from the inlet to the outlet, the inner and outer bodieshaving offset inner and outer axes respectively, at least one of theinner and outer bodies being rotatable about a corresponding one of theinner and outer axes, the inner and outer bodies having intermeshedinner and outer helical blades wound about the inner and outer axesrespectively, the inner and outer helical blades extending radiallyoutwardly and inwardly respectively, the core assembly having first,second, and third sections in serial downstream flow relationshipextending between the inlet and the outlet, the inner and outer helicalblades having first, second, and third twist slopes in the first,second, and third sections respectively, the first twist slopes beingless than the second twist slopes and the third twist slopes being lessthan the second twist slopes, and a combustion section extending axiallydownstream from the second section through at least a portion of thethird section.
 28. An engine as claimed in claim 27 further comprisingthe inner helical blade in the first section having a sufficient numberof turns to trap charges of air in the first section during thegenerator's operation.
 29. An engine as claimed in claim 28 furthercomprising the number of turns being enough to mechanically trap thecharges of air.
 30. An engine as claimed in claim 28 further comprisingthe number of turns being enough to dynamically trap the charges of air.31. An engine as claimed in claim 27 further comprising the outer bodybeing rotatable about the outer axis and the inner body and beingrotatable about the inner axis.
 32. An engine as claimed in claim 31further comprising the inner and outer bodies being geared together in afixed gear ratio.
 33. An engine as claimed in claim 32 furthercomprising the inner helical blade in the first section having asufficient number of turns to trap charges of air in the first sectionduring the generator's operation.
 34. An engine as claimed in claim 33further comprising the number of turns being enough to mechanically trapthe charges of air.
 35. An engine as claimed in claim 33 furthercomprising the number of turns being enough to dynamically trap thecharges of air.
 36. An engine as claimed in claim 27 further comprisingthe outer body being rotatably fixed about the outer axis and the innerbody being orbital about the outer axis.
 37. An engine as claimed inclaim 36 further comprising the inner helical blade in the first sectionhaving a sufficient number of turns to trap charges of air in the firstsection during the generator's operation.
 38. An engine as claimed inclaim 37 further comprising the number of turns being enough tomechanically trap the charges of air.
 39. An engine as claimed in claim37 further comprising the number of turns being enough to dynamicallytrap the charges of air.
 40. An aircraft gas turbine engine comprising:a fan section and a core engine including a gas generator downstream ofthe fan section, a low pressure turbine having at least one row of lowpressure turbine rotor blades downstream of the gas generator, the lowpressure turbine drivingly attached to at least one row ofcircumferentially spaced apart fan rotor blades in the fan section by ashaft, the gas generator including an inlet axially spaced apart andupstream from an outlet, a core assembly including an inner bodydisposed within an outer body and the inner and outer bodies extendingfrom the inlet to the outlet, the inner and outer bodies having offsetinner and outer axes respectively, the inner and outer bodies beingrotatable about the inner and outer axes respectively, the inner andouter bodies having intermeshed inner and outer helical blades woundabout the inner and outer axes respectively, the inner and outer helicalblades extending radially outwardly and inwardly respectively, the coreassembly having first, second, and third sections in serial downstreamflow relationship extending between the inlet and the outlet, the innerand outer helical blades having first, second, and third twist slopes inthe first, second, and third sections respectively, the first twistslopes being less than the second twist slopes and the third twistslopes being less than the second twist slopes, and a combustion sectionextending axially downstream from the second section through at least aportion of the third section.
 41. An engine as claimed in claim 40further comprising the inner helical blade in the first section having asufficient number of turns to trap charges of air in the first sectionduring the generator's operation.
 42. An engine as claimed in claim 41further comprising the number of turns being enough to mechanically trapthe charges of air.
 43. An engine as claimed in claim 41 furthercomprising the number of turns being enough to dynamically trap thecharges of air.
 44. An engine as claimed in claim 40 further comprisingthe inner and outer bodies being geared together in a fixed gear ratio.45. An engine as claimed in claim 44 further comprising the innerhelical blade in the first section having a sufficient number of turnsto trap charges of air in the first section during the generator'soperation and the number of turns being enough to mechanically trap thecharges of air.